Ayer was also a secular humanist. He was honorary associate of the Rationalist Press Association after 1947, and a successor to evolutionary biologist and humanist Julian Huxley when he became president of the British Humanist Association. In 1965, Ayer was named the first president of the Agnostics’ Adoption Society. He edited the anthology The Humanist Outlook in 1965.

At the peak of his career, Ayer served as a sort of in-house atheist for the British Broadcasting Corporation. He debated the Jesuit philosopher Frederick Copleston (1907–1994) on the subject of religion. Copleston was the author of the nine-volume History of Philosophy (1946–1975), so the two were matched in erudition.

Ayer (apparently briefly) revised his life-long atheism after a near-death experience in 1989—brought on by choking on a piece of smoked salmon. Toward the end of his life, though, he said, “What I should have said is that my experiences have weakened, not my belief that there is no life after death, but my inflexible attitude towards that belief.”

In Language, Truth and Logic (1936), published when he was just 26, Ayer forcefully and with great panache presented the main tenets of logical positivism as a doctrine broadly relevant to philosophy. He asserted the empiricist doctrine that all of our knowledge of the world comes from sensory experience. The truth or falsity of statements was dependent on whether they could be verified in terms of that experience. Only statements that could be true or false were meaningful. It followed from these bold claims that metaphysical, religious, and ethical statements, if they were not true by definition, could assert nothing meaningful about reality. Statements about the self, the external world, and the minds of others had to be confirmed by sensory experience, if they were to be meaningful. Concerning the existence of God, for example, Ayer maintained that the question itself was not meaningful because no possible experience could determine its truth or falsity. Ayer’s ethical theory was emotivist, that is, ethical judgments were held to be expressions of emotions.